This invention relates to airfoils, and particularly to airfoils used in fans.
FIG. 1a illustrates a typical prior art airfoil 8 having a leading edge 10, a trailing edge 12, and substantially parallel surfaces 14, 16. As shown in FIG. 1b, when airfoil 8 contacts a stream of air 17, the air stream engages leading edge 10, and separates into streams 18, 20. Stream 18 passes along surface 14 while stream 20 passes along surface 16. As is well known, stream 18 travels a greater distance than stream 20, with that result that air adjacent to surface 16 is at a higher pressure than air adjacent to surface 14. Consequently, surface 16 is referred to as the "pressure side" of the airfoil, and surface 14 is referred to as the "suction side" of the airfoil.
Noise is generated by airfoils due to pressure fluctuations in the air passing over each of the airfoil surfaces. The noise level can be reduced by increasing the thickness of the airfoil. However, the weight of the airfoil increases as it becomes thicker thereby increasing manufacturing costs and decreasing performance.